- What is ToF?
- ToF transmission/reception block diagram
- Noise issues affecting ToF
- Power supply noise suppression using ferrite beads
- Ferrite beads recommended for noise suppression
- Confirming the effects of ferrite bead insertion
- Confirmation of effectiveness of ferrite bead insertion - ripple noise
- Confirmation of effectiveness of ferrite bead insertion - transient response
- Confirmation of effectiveness of ferrite bead insertion - VCSEL current waveform
3. Noise issues affecting ToF
As shown in the figure below, a large current suddenly flows through the driver circuit when a steep, high-output pulse is emitted, and this can easily cause a large voltage spike to form on the power line.
There is a concern that the noise generated in this way could interfere with the receiver and degrade the sensitivity of the ToF sensor.
Most noise emissions can be prevented with shielding, but it is also necessary to take measures to prevent conduction of noise via the power line.
In this section we introduce an EMI filter as an effective way to suppress noise conduction.
4. Power supply noise suppression using ferrite beads
Inserting ferrite beads is an effective way of dealing with noise issues of this sort.
By inserting ferrite beads near the VCSEL and laser driver, it is possible to reduce the amplitude of noise spikes that leak into the power line.
In addition, by inserting ferrite beads in the ground line between the transmitter and receiver, it is possible to prevent noise from being transmitted via the ground.
- Insertion of ferrite beads in the portion of the transmitter where the power current enters to suppress noise conduction via the power line
- Insertion of ferrite beads in the portion of the receiver connected to the ground to suppress noise conduction via the ground line
5. Ferrite beads recommended for noise suppression
Selected with an awareness of noise frequencies that can easily cause problems.
Select the optimal part numbers to match the available mounting space.